1. Field of the Invention
The present invention relates to battery-powered electronic devices, and more particularly to apparatus and methods for controlling a power supply to battery-powered portable electronic devices.
2. Background of the Invention
Portable electronic devices, such as portable computers, camcorders, mobile phones, cassette tape recorders and other devices, operate with batteries. Typically, these devices are also capable of using AC (alternating current) power. Battery power is used when AC power is not convenient or not available. Most battery-powered electronics have circuitry for displaying the remaining capacity of a battery to a user. If the remaining battery capacity is less than a preset value, the user is warned of a low battery condition.
A successive use time of a battery-powered portable electronic device is very important. Some portable electronic devices each have two batteries in order to extend the use time thereof. Either one or both of the two batteries can be mounted on such devices. Also, some recent portable stereo cassette tape players permit a combined and simultaneous use of both a non-rechargeable primary battery and a rechargeable secondary battery.
Upon using such an electronic device to accommodate two batteries, when a first battery is discharged, a user may mount a second battery on the device without removing the first discharged battery in order to prolong the usage time of the device. In this case, the usage time of the second battery will lessen since the voltage levels of the two batteries are different from each other so that a relatively higher voltage level of the second battery is rapidly lowered to a relatively lower voltage level of the first battery.
An example of portable electronic devices operating with two batteries is disclosed in U.S. Pat. No. 5,867,007 to Kim entitled Selection Circuit for Dual Batteries in a Battery Powered Electronic Device. Kim ""007 discloses a battery selection circuit for dual battery packs. The battery selection circuit includes a battery detector for sensing the existence of the first and second battery packs and for producing the detect signals corresponding thereto. These detect signals are provided to a microcontroller to produce first and second battery discharge enable signals. In response to the first and second battery discharge enable signals, first and second electronic switches respectively connect each power supply line from the first and second batteries to a power supply circuit of the device.
U.S. Pat. No. 5,477,123 to Allen et al. entitled Connection Multiple Batteries to Battery Powered Devices, discloses a circuit for serially connecting multiple batteries to a battery-powered device so that the device will serially charge or discharge the batteries. The device includes at least two controllable switch circuits for selectively connecting batteries to the battery-powered device, a power flow sensor for sensing power flow from the device to the selected battery or vice-versa, and a selector circuit for sequentially enabling the switch circuits to sequentially connect the batteries to the battery-powered device so that the batteries will sequentially charge or discharge.
U.S. Pat. No. 5,485,073 to Kasashima et al. entitled Personal Computer for Performing Charge and Switching Control of Different Types of Battery Packs, discloses a personal computer having a battery pack mounting section for detachably receiving battery packs having different current capacities. It is disclosed when the PC-CPU detects that the currently used battery pack is in a low-battery state, it selects the other battery pack to supply the operating power to the personal computer.
U.S. Pat. No. 5,621,301 to Allen et al. entitled Connecting Multiple Batteries to Battery Powered Devices, discloses a circuit serially connecting multiple batteries to a battery-powered device so that the device will serially charge or discharge the batteries. The device includes at least two controllable switch circuits for selectively connecting batteries to the battery-powered device, a power flow sensor for sensing power flow from the device to the selected battery or vice-versa, and a selector circuit for sequentially enabling the switch circuits to sequentially connect the batteries to the battery-powered device so that the batteries will sequentially charge or discharge.
U.S. Pat. No. 5,646,503 to Stockstad entitled Method for Balancing Power Sources and Structure Thereof discloses a power source balancing circuit that balances two power sources such as two battery cells. When the power source balancing circuit is enabled, it compares a current flowing through the first battery cell and a first resistor with a current flowing through the second battery cell and a second resistor. If a current difference larger than a predetermined limit is detected, the battery cell with a higher voltage is discharged through a corresponding discharge resistor by switching on a corresponding switch.
U.S. Pat. No. 4,140,957 to Rapp entitled Calculator Driving and Battery Pack Recharging Circuit, discloses a circuit to drive an electronic calculator from a source of ac power or, alternately, from either one of a plurality of disposable batteries or a unique, rechargeable battery pack. When disposable batteries are deposited inside the battery compartment of the calculator and an ac adapter accessory is connected to provide power to the calculator, the disposable batteries are electrically isolated from the ac source, and when the rechargeable battery pack is deposited inside the battery compartment of the calculator and the ac adapter is connected to provide power to the calculator, the battery pack is recharged.
U.S. Pat. No. 5,300,874 to Shimamoto et al. entitled Intelligent Power Supply System for a Portable Computer, discloses a power supply system for a portable computer, the computer having a central processing unit (CPU), and being operable in response to power supplied from at least two chargeable batteries or an alternating current (AC) adapter, includes means for detachably coupling the batteries to the computer and a PC-CPU for controlling power supply independent of the CPU. The PC-CPU has means for receiving battery select information for controlling power supply and generating a control signal. The power supply system further includes battery control circuit means, connected to the AC adapter and the batteries, for selecting and controlling the AC adapter or one of the batteries based on the control signal.
U.S. Pat. No. 5,986,437 to Lee entitled Power Supply System for Portable Electronic Devices, discloses a power supply system for a portable device such as potable personal computer, to be operated from a DC power source supplied from a rechargeable battery or an AC adapter. The power supplying system includes an input current detecting circuit for detecting an input current supplied from the AC adapter and for generating a detection signal having a magnitude which varies depending upon the input current and a charging current control circuit for controlling the amount of the charging current in response to the detection signal.
Also, of interest in relation to supplying power to a battery powered electronic device are: U.S. Pat. No. 5,179,337 to Staarman et al. entitled Over-Discharge Protection for Rechargeable Batteries; U.S. Pat. No. 5,355,071 to Ishida et al. entitled Power Source Apparatus for Vehicles; U.S. Pat. No. 5,359,318 to Asai et al. entitled Hand-Held Electronic Apparatus Using Two Batteries Sequentially Supplying Current to Inductive Element; U.S. Pat. No. 5,477,124 to Tamai entitled Circuit to Prevent Excessive Rechargeable Battery Discharge; U.S. Pat. No. 5,547,775 to Eguchi et al. entitled Circuit for Preventing Overcharge and Over discharge of Secondary Batteries, U.S. Pat. No. 5,553,294 to Nanno et al. entitled Portable Computer Powered by Rechargeable Batteries; U.S. Pat. No. 5,598,041 to Willis entitled Efficient Fault Tolerant Switching Circuit for Redundant D.C. Power Supplies; U.S. Pat. No. 5,629,602 to Makino entitled Portable Electronic Equipment with Attachment for Supplying Power and Charging Battery; U.S. Pat. No. 5,652,499 to Morita et al. entitled Power Supply Apparatus to Provide Power to Electrical Equipment from a Plurality of Battery Packs and Its Method of Power Supply; U.S. Pat. No. 5,239,495 to Nanno et al. entitled Power Supply Control System for a Portable Computer; U.S. Pat. No. 5,355,073 to Nguyen entitled Battery Pack Sensor for an AC Adapter; U.S. Pat. No. 5,383,140 to Nanno et al. entitled Power Supply Control System for a Portable Computer; U.S. Pat. No. 5,455,562 to Chin entitled Home Intruder Indicator 2; U.S. Pat. No. 5,581,772 to Nanno et al. entitled Power Supply Control System for a Portable Computer; and U.S. Pat. No. 5,955,797 to Kim entitled Portable Computer Being Powered by Either a Battery Pack or an AC Adapter.
Therefore, it is an object, among other objects, of the present invention to provide an electronic device simultaneously accommodating two batteries, which is capable of maximizing the usage time of the batteries.
According to an aspect of the invention, when voltage levels of two batteries mounted in an electronic device are different, one battery having a relatively higher voltage level is discharged in advance of the other battery. Thereafter, when the two batteries have the same voltage levels, they are simultaneously discharged.
In a preferred embodiment, among embodiments, of the present invention, an electronic device includes a power input terminal for supplying power to a main circuit of the electronic device, a first battery and a second battery, a battery control circuit for generating a battery selection control signal in response to output voltages of the first battery and the second battery, and a battery selection circuit for electrically connecting one of the two batteries that has a relatively higher voltage level to the power input terminal in response to the battery selection control signal.
The battery selection circuit includes a first switch circuit and a second switch circuit. The first switch circuit is connected between the first battery and the power input terminal, and is selectively turned on and off in response to the battery selection control signal. The second switch circuit is connected between the second battery and the power input terminal, and is selectively turned on and off in response to the battery selection control signal. The first switch circuit and the second switch circuit are alternatively, or selectively, turned on and off.
The electronic device further includes an AC (alternating current) adapter for supplying power to the power input terminal, and an adapter detection circuit. The battery selection circuit further includes a third switch circuit connected to the power input terminal and between the first switch circuit and the second switch circuit. The adapter detection circuit detects whether the AC adapter is connected to the power input terminal, and generates an adapter detection signal when the AC adapter is connected to the power input terminal. The third switch circuit is selectively turned on and off in response to the adapter detection signal. When the AC adapter is connected to the power input terminal, the first and second switch circuits are turned off in response to the adapter detection signal.
The electronic device further includes a battery voltage detection circuit connected to the first and second batteries. When an output voltage of the first battery or the second battery is below a preset value, the battery voltage detection circuit generates a low voltage detection signal, and then supplies it to the main circuit.
The battery voltage detection circuit includes a low voltage detection circuit for generating the low voltage detection signal when an input voltage level at a voltage input terminal to the low voltage detection circuit is lower than a predetermined level, a first diode connected to both the voltage input terminal of the low voltage detection circuit and the first battery, and a second diode connected to the voltage input terminal of the low voltage detection circuit and the second battery.
The battery control circuit includes a first voltage divider for dividing an output voltage of the first battery, a second voltage divider for dividing an output voltage of the second battery, and a comparator for comparing an output of the first voltage divider with an output of the second voltage divider to generate the battery selection control signal.
According to another aspect, among aspects, of the present invention, in a battery-powered electronic device having a first battery and a second battery, it is determined whether the first and second batteries are simultaneously mounted on or electrically connected to the electronic device. If only one of the first and second batteries is mounted on or electrically connected to the device, the electronic device is supplied with power from the mounted or connected battery. When the first and second batteries are mounted on or electrically connected to the electronic device, it is determined whether output voltages of the first and second batteries are different from each other. If so, the electronic device is supplied with power from one of the two batteries that has a relatively higher output voltage. If the output voltages of the first and second batteries are same, the electronic device is supplied with power from both the first and the second batteries. When an AC adapter is connected to the electronic device, power supplied from any of the first battery and the second battery to the electronic device is cut off.